U.S. patent number 7,966,884 [Application Number 12/017,565] was granted by the patent office on 2011-06-28 for two-dimensional-array ultrasonic probe and ultrasonic diagnostic system.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba, Toshiba Medical Systems Corporation. Invention is credited to Hiroyuki Shikata.
United States Patent |
7,966,884 |
Shikata |
June 28, 2011 |
Two-dimensional-array ultrasonic probe and ultrasonic diagnostic
system
Abstract
A two-dimensional array ultrasonic probe has an ultrasonic
transducer. The transducer has transducer elements that are
arranged in a first direction and a second direction, forming a
lattice. Acoustic-emission electrodes are provided on the
acoustic-emission surfaces of the transducer elements. Back
electrodes are provided on the backs of the transducer elements. A
transmitting-circuit unit is connected to the acoustic-emission
electrodes. A receiving-circuit unit is connected to the back
electrodes. Of the acoustic-emission electrodes, two electrodes are
short-circuited to the transmitting circuits of the
transmitting-circuit unit. The remaining two acoustic-emission
electrodes are short-circuited to the receiving circuits of the
receiving-circuit unit.
Inventors: |
Shikata; Hiroyuki
(Nasushiobara, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Tokyo, JP)
Toshiba Medical Systems Corporation (Otawara-shi,
JP)
|
Family
ID: |
39639964 |
Appl.
No.: |
12/017,565 |
Filed: |
January 22, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080173094 A1 |
Jul 24, 2008 |
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Foreign Application Priority Data
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Jan 23, 2007 [JP] |
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2007-012842 |
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Current U.S.
Class: |
73/625;
73/626 |
Current CPC
Class: |
A61B
8/4494 (20130101); B06B 1/0629 (20130101) |
Current International
Class: |
G01N
29/04 (20060101) |
Field of
Search: |
;73/625,626,634,618,620
;600/459 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Saint Surin; Jacques M
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
What is claimed is:
1. An ultrasonic probe comprising: a plurality of ultrasonic
transducer elements, each of which has a first electrode and a
second electrode provided on an acoustic-emission surface and a
back, respectively; transmitting circuits each of which is
connected to one of the first and second electrodes; and receiving
circuits each of which is connected to the other of the first and
second electrodes, wherein at least two of adjacent ultrasonic
transducer elements are short-circuited to each other by the first
and second electrodes, and the first and second electrodes achieve
short-circuiting in different patterns.
2. The ultrasonic probe according to claim 1, wherein the
ultrasonic transducer elements are arranged in a direction
intersecting at right angles with the acoustic-emission surface,
and form a one-dimensional array.
3. The ultrasonic probe according to claim 1, wherein the number of
transducer elements short-circuited by the first electrode is
different from the number of transducer elements short-circuited by
the second electrode.
4. The ultrasonic probe according to claim 1, wherein the adjacent
transducer elements are short-circuited by the first electrode, and
other adjacent transducer elements are short-circuited by the
second electrode.
5. The ultrasonic probe according to claim 1, wherein the number of
transducer elements short-circuited by one of the first and second
electrodes is twice the number of transducer elements
short-circuited by the other of the first and second
electrodes.
6. The ultrasonic probe according to claim 1, wherein the number of
transducer elements short-circuited by one of the first and second
electrodes is 1.5 times the number of transducer elements
short-circuited by the other of the first and second
electrodes.
7. The ultrasonic probe according to claim 1, wherein two adjacent
transducer elements are short-circuited by the first electrode and
the second electrode.
8. The ultrasonic probe according to claim 1, wherein the
ultrasonic transducer elements are arranged in a plane intersecting
at right angles with an acoustic-emission direction, and form a
two-dimensional array.
9. The ultrasonic probe according to claim 1, wherein the
ultrasonic transducer elements are arranged in a honeycomb pattern,
in a plane intersecting at right angles with an acoustic-emission
direction, and form a two-dimensional array.
10. The ultrasonic probe according to claim 1, wherein the
ultrasonic transducer elements are arranged in two directions
intersecting at right angles with each other and with an
acoustic-emission direction, and form a two-dimensional array
shaped like a lattice.
11. The ultrasonic probe according to claim 10, wherein the
short-circuiting by the first electrode and the short-circuiting by
the second electrode are achieved, each by short-circuiting
adjacent ultrasonic transducer elements, and the direction in which
the ultrasonic transducer elements are short-circuited by the first
electrode and the direction in which the ultrasonic transducer
elements are short-circuited by the second electrode intersect at
right angles with each other.
12. The ultrasonic probe according to claim 10, wherein the
short-circuiting by the first electrode and the short-circuiting by
the second electrode are achieved, each by short-circuiting
adjacent two ultrasonic transducer elements, and the direction in
which the ultrasonic transducer elements are short-circuited by the
first electrode and the direction in which the ultrasonic
transducer elements are short-circuited by the second electrode
intersect at right angles with each other.
13. The ultrasonic probe according to claim 10, wherein the
short-circuiting by the first electrode is achieved by
shorting-circuiting two ultrasonic transducer elements arranged in
a first direction and three ultrasonic transducer elements arranged
in a second direction intersecting at right angles with the first
direction, and the short-circuiting by the second electrode is
achieved by shorting-circuiting three ultrasonic transducer
elements arranged in the first direction and two ultrasonic
transducer elements arranged in the second direction.
14. The ultrasonic probe according to claim 1, wherein the
short-circuiting by the first and second electrodes is achieved by
using conductor patterns provided on a printed circuit board that
is connected directly or via an adjustment layer to the ultrasonic
transducer elements.
15. The ultrasonic probe according to claim 14, wherein the printed
circuit board is a flexible printed circuit board which is composed
of a base made of polyimide film and a conductor pattern made of
copper foil and formed on the base.
16. The ultrasonic probe according to any one of claims 1, 2, 8, 9
and 14, wherein transmitting circuits are connected, each to one of
the first and second electrodes, and receiving circuits are
connected, each to the other of the first and second
electrodes.
17. The ultrasonic probe according to claim 1, wherein the
short-circuiting to the first electrode and the short-circuiting by
the second electrode are achieved, each by a transmitting/receiving
circuit board connected to the ultrasonic transducer elements.
18. An ultrasonic diagnostic system having an ultrasonic probe
designed to apply and receive ultrasonic waves to and from a
subject, thereby to acquire information about tissues existing in
the subject, wherein the ultrasonic probe comprises a plurality of
ultrasonic transducer elements, each of which has a first electrode
and a second electrode provided on an acoustic-emission surface and
a back, respectively, transmitting circuits each of which is
connected to one of the first and second electrodes, and receiving
circuits each of which is connected to the other of the first and
second electrodes; and the first and second electrodes
short-circuit at least two of at least two adjacent ultrasonic
transducer elements, respectively in different patterns.
19. The ultrasonic diagnostic system according to claim 18, wherein
the ultrasonic transducer elements are arranged in a direction
intersecting at right angles with an acoustic-emission surface, and
form a one-dimensional array.
20. The ultrasonic diagnostic system according to claim 18, wherein
the ultrasonic transducer elements are arranged in a honeycomb
pattern, in a plane intersecting at right angles with an
acoustic-emission direction, and form a two-dimensional array.
21. The ultrasonic diagnostic system according to claim 18, wherein
the ultrasonic transducer elements are arranged in two directions
intersecting at right angles with each other and with an
acoustic-emission direction, and form a two-dimensional array
shaped like a lattice.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from prior Japanese Patent Application No. 2007-012842, filed Jan.
23, 2007, the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus
that transmits ultrasonic waves to a patient, receives the waves
reflected from the patient and processes the waveforms received,
thereby displaying, on a screen, tomograms for use in making a
diagnosis. More particularly, this invention relates to a
two-dimensional ultrasonic probe to be connected to an ultrasonic
diagnostic apparatus that can provide three-dimensional images in
real time, and also to an ultrasonic diagnostic system.
2. Description of the Related Art
Any ultrasonic probe comprises a two-dimensional array transducer
that has elements arranged in the form of a two-dimensional
lattice.
A conventional two-dimensional array transducer comprises a backing
material and a plurality of ultrasonic transducer elements. The
transducer elements 6 are arranged on the backing material, in the
form of a two-dimensional lattice. Two electrodes are provided for
each transducer element. One electrode is provided on the acoustic
emission surface of the element, and the other electrode is
provided on the back of the element, which contacts backing
material. These electrodes are connected to transmitting circuits
(not shown) and receiving circuits (not shown). Further, an
acoustic member, such as an acoustic adjustment layer, an acoustic
lens or a bio-contact member, is arranged on the acoustic emission
surface of each transducer element.
FIG. 1 is a block diagram presenting the configuration of a
conventional ultrasonic diagnostic system.
As FIG. 1 shows, the ultrasonic diagnostic system comprises an
ultrasonic probe 10a and an ultrasonic diagnostic apparatus 20. The
ultrasonic probe 10a has a two-dimensional array transducer 2, a
transmitter/receiver disconnecting circuit 12, a transmitting
circuit 14, a receiving circuit 16, and a connector 18. The
ultrasonic diagnostic apparatus 20 has a control circuit 22, a
signal-processing circuit 24, and a display 26.
The two-dimensional array transducer 2 has transducer elements,
each connected to a signal line. The signal line is connected to
the transmitting circuit (balser) 14 and the receiving circuit
(receiver) 16, both provided in the ultrasonic probe la or in the
ultrasonic diagnostic apparatus 20. (In the case shown in FIG. 1,
the transmitting circuit 14 and the receiving circuit 16 are
provided in the ultrasonic probe 10a.) In the ultrasonic diagnostic
apparatus 20, the signal-processing circuit 24 performs
analog-to-digital conversion on the signal that the receiver 16 has
received, so that a tomogram may be displayed on the display 26
(e.g., CRT monitor) after an envelope, for example, has been
detected. Further, since the two-dimensional array transducer can
transmit and receive ultrasonic waves coming in any directions in
space, the signal can be converted to data representing a tomogram
of any desired region or can be subjected to three-dimensional
rendering. Hence, the display 26 can display a tomogram or a
three-dimensional image in real time.
In the conventional one-dimensional array transducer, the
strip-shaped transducer elements are linearly arranged. About 100
elements are so arranged in most cases. By contrast, in any
two-dimensional array transducer, thousands of transducer elements
are arranged in rows and columns, and the probe cable is thick if
it contains the signal lines of all transducer elements. The
thicker the probe cable, the lower the operability of the
ultrasonic probe having the two-dimensional array transducer. In
view of this, most ultrasonic probes incorporate transmitting
circuits and receiving circuits.
Two electrodes are provided, respectively, on the acoustic emission
surface and back of each element of a two-dimensional array
transducer. In most two-dimensional array transducers, the
electrodes provided on the acoustic emission surfaces are bundled
together and connected to the transmitting circuit and receiving
circuit through a transmitter/receiver disconnecting circuit,
whereas the electrodes provided on the backs are connected,
independently of one another, to the transmitting circuit and
receiving circuit through the transmitter/receiver disconnecting
circuit. In this case, the voltage of the pulses transmitted is
generally 100V or more. This voltage raises breakdown problems in
most ICs manufactured by the ordinary process of producing
low-breakdown-voltage devices.
Therefore, the transmitter/receiver disconnecting circuit is
constituted by an IC manufactured by a special process of producing
high breakdown-voltage devices. The transmitter/receiver
disconnecting circuit is inevitably not only expensive, but is also
large and consumes much power. If incorporated into a probe, the
probe will be large and have low operability. Further, the
transmission voltage must be reduced to keep the probe temperature
below a prescribed value, thereby ensuring safety. If the
transmission voltage is so reduced, the sensitivity of the probe
will decrease. Consequently, the probe will raise problems in terms
of image quality.
In view of the above, the transmitting circuit 14 and the receiving
circuit 16 may be connected, respectively, to the electrodes 2a
provided on the acoustic emission surface of the transducer 2 and
be connected to the electrodes 2a provided on the back of the
transducer 2, as is shown in FIG. 2. In this case, the receiving
circuit 16 is held short-circuited while the transmitting circuit
14 is transmitting a signal, and transmitting circuit 14 is held AC
short-circuited, while the receiving circuit 16 is receiving a
signal. The transmitting circuit 14 and the receiving circuit 16
are thus disconnected from each other. Such an ultrasonic probe as
shown in FIG. 2 is disclosed in, for example, Jpn. Pat. Appln.
KOKAI Publication No. 2004-41730. In this technique, the transducer
can, by itself, disconnect the transmitting circuit and the
receiving circuit from each other. A transmitter/receiver
disconnecting circuit need not be used at all. The receiving
circuit can be an inexpensive IC manufactured by the ordinary
process of producing low breakdown-voltage devices. In addition,
since no transmitter/receiver disconnecting circuit is required,
the ultrasonic probe can be smaller and consumes less power.
Even if the technique disclosed in the Jpn. Pat. Appln. KOKAI
Publication No. 2004-41730 is employed, however, transmitting
circuits and receiving circuits must be provided in the same
numbers as the transducer elements. In order to prevent an increase
in the size of the circuitry provided in the probe, the total
number of elements should be smaller than a certain value.
Generally, it is necessary to raise the frequency or increase the
aperture in order to attain a high resolution. If the frequency is
raised or the aperture is increased, while using a limited number
of transducer elements, however, the product of the frequency and
the pitch of elements will inevitably increase. Consequently, the
grating lobe, i.e., transmission or reception in a direction other
than the intended direction, become prominent. Hence, the frequency
cannot be raised or the aperture cannot be increased in order to
attain a high resolution.
In order to attain a large aperture, transmitting circuits and
receiving circuits may be used in smaller numbers and a limited
number of channels may be connected to these transmitting and
receiving circuits. This technique (known as sparse arraying)
decreases the ratio of the effective transmission-reception area to
the aperture area, reducing the sensitivity of the probe or
generates side lobes in the same way as grating lobes are
generated. The side lobes decrease the resolution, because they
extend in various directions.
BRIEF SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a
two-dimensional array ultrasonic probe that has as small a
transmitting-circuit section and a receiving-circuit section as
possible and yet has a large aperture and high sensitivity, not
influenced by grating lobes, and to provide an ultrasonic
diagnostic system that has such a two-dimensional array ultrasonic
probe.
An ultrasonic probe according to the present invention comprises: a
plurality of ultrasonic transducer elements, each of which has a
first electrode and a second electrode provided on an
acoustic-emission surface and a back, respectively; transmitting
circuits each of which is connected to one of the first and second
electrodes; and receiving circuits each of which is connected to
the other of the first and second electrodes. At least two of
ultrasonic transducer elements are short-circuited to at least one
of the first and second electrodes, and the first and second
electrodes achieves short-circuiting in different patterns.
An ultrasonic diagnostic system according to the present invention
has an ultrasonic probe designed to apply and receive ultrasonic
waves to and from a subject, thereby to acquire information about
tissues existing in the subject. The ultrasonic probe comprises a
plurality of ultrasonic transducer elements, each of which has a
first electrode and a second electrode provided on an
acoustic-emission surface and a back, respectively, transmitting
circuits each of which is connected to one of the first and second
electrodes, and receiving circuits each of which is connected to
the other of the first and second electrodes. The first and second
electrodes are short-circuited to different ultrasonic transducer
elements, respectively.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate embodiments of the
invention, and together with the general description given above
and the detailed description of the embodiments given below, serve
to explain the principles of the invention.
FIG. 1 is a block diagram presenting the configuration of a
conventional ultrasonic diagnostic system;
FIG. 2 is a block diagram presenting a conventional ultrasonic
diagnostic system of a different configuration;
FIG. 3 is a perspective view representing the configuration of the
transducer unit of a two-dimensional array ultrasonic probe
according to a first embodiment of the present invention;
FIG. 4 is a perspective view showing a pattern in which the
electrodes of the transducer unit are arranged in the first
embodiment of the invention;
FIG. 5 is a diagram showing the configuration of an ultrasonic
diagnostic system including the ultrasonic probe according to the
first embodiment of the invention;
FIG. 6 is a perspective view showing a different ultrasonic
transducer unit that may be incorporated in the two-dimensional
array ultrasonic probe according to the first embodiment;
FIGS. 7A and 7B are plan views representing patterns in which the
electrodes are arranged in the two-dimensional array probe
according to the first embodiment, FIG. 7A showing the electrode
pattern on the acoustic emission surface, and FIG. 7B showing the
electrode pattern on the back;
FIGS. 8A to 8C are diagrams depicting the sound fields that an
ordinary two-dimensional array probe may have;
FIGS. 9A to 9C are diagrams depicting the sound fields that may be
generated if two transmitting circuits are connected in parallel in
the Y-direction and two receiving circuits are connected in
parallel in the X-direction;
FIGS. 10A to 10C are diagrams depicting the sound fields that the
two-dimensional array probe according to the first embodiment of
this invention may have;
FIGS. 11A and 11B are plan views representing patterns in which the
electrodes are arranged in a two-dimensional array probe according
to a second embodiment, FIG. 11A showing the electrode pattern on
the acoustic emission surface, and FIG. 11B showing the electrode
pattern on the back;
FIGS. 12A to 12C show the arrangement of the transducer elements of
a two-dimensional array ultrasonic probe according to a third
embodiment of this invention, FIG. 12A being a perspective view of
the probe, FIG. 12B being a perspective view showing the electrode
pattern of the probe, and FIG. 12C being a plan view showing the
electrode pattern of the probe;
FIG. 13 is a perspective view showing the configuration of the
transducer unit of a one-dimensional array ultrasonic probe
according to a fourth embodiment of this invention; and
FIG. 14 is a diagram depicting a sound field having a sound field
that the one-dimensional array ultrasonic probe according to the
fourth embodiment may have.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described, with
reference to the accompanying drawings.
First Embodiment
FIG. 3 is a perspective view representing the configuration of the
transducer unit of a two-dimensional array ultrasonic probe
according to the first embodiment of the present invention.
As shown in FIG. 3, the transducer unit 30 of the two-dimensional
array ultrasonic probe comprises a backing material 32 and a
plurality of ultrasonic transducer elements 34. The transducer
elements 34 are arranged on the backing material 32, in the form of
a two-dimensional lattice. Electrodes are provided on the acoustic
emission surfaces of the elements 34, and other electrodes are
provided on the backs of the elements 34, which contact backing
material 32. These electrodes are connected to transmitting
circuits (not shown) and receiving circuits (not shown). Further,
an acoustic member, such as an acoustic adjustment layer, an
acoustic lens or a bio-contact member, is arranged on the acoustic
emission surface of each transducer element 34.
FIG. 4 is a perspective view showing a pattern in which the
electrodes are arranged with respect to the ultrasonic transducer
elements 34 in the first embodiment of the invention. In FIG. 4,
the ultrasonic transducer elements (hereinafter referred to as
piezoelectric elements) 34 are shown as if separated from the
electrodes 36 provided on the acoustic emission surfaces and from
the electrodes 38 provided on the backs. In this embodiment, any
two adjacent piezoelectric elements 34 arranged in a first
direction are short-circuited by one electrode 36 provided on their
acoustic emission surfaces, and any two adjacent piezoelectric
elements 34 arranged in a second direction intersecting at right
angles with the first direction are short-circuited by one
electrode 38 provided on their backs.
Transmitting circuits (not shown) are connected to the
acoustic-emission electrodes 36 and receiving circuits are
connected to the back electrodes, by a signal-line board, such as a
flexible printed-circuit (FPC) board (not shown in FIG. 4). As a
result, the two-dimensional array ultrasonic transducer unit 30 has
such a circuit configuration as shown in FIG. 5.
FIG. 5 is a diagram showing the configuration of an ultrasonic
diagnostic system that includes an ultrasonic probe according to a
first embodiment of the present invention.
FIG. 5 shows only four ultrasonic transducer elements 44a to 44d.
The transducer element 44a comprises a piezoelectric element 34a,
an acoustic-emission electrode 36a, and a back electrode 38a. The
transducer element 44b comprises a piezoelectric element 34b, an
acoustic-emission electrode 36b, and a back electrode 38b. The
transducer element 44c comprises a piezoelectric element 34c, an
acoustic-emission electrode 36c, and a back electrode 38c. The
transducer element 44d comprises a piezoelectric element 34d, an
acoustic-emission electrode 36d, and a back electrode 38d. Two
transmitting circuits 48.sub.1 and 48.sub.2 provided in a
transmitting-circuit unit 48 are connected by an FPC board 54.
Similarly, two receiving circuits 50.sub.1 and 50.sub.2 provided in
a receiving-circuit unit 50 are connected by an FPC board 56. The
FPC board 54 and the FPC board 56, which are flexible printed
circuit boards, are composed of a base made of polyimide film and a
conductor pattern made of copper foil and formed on the base. The
two ultrasonic transducer elements connected to which one
transmitting circuit is connected differ from the two ultrasonic
transducer elements to which one receiving circuit is
connected.
For example, the transmitting circuit 48.sub.1 is connected by the
FPC board 54 to the acoustic-emission electrode 36a of the
transducer element 44a and the acoustic-emission electrode 36c of
the transducer element 44c, and the transmitting circuit 48.sub.2
is connected by the FPC board 54 to the acoustic-emission electrode
36b of the transducer element 44b and the acoustic-emission
electrode 36d of the transducer element 44d. The receiving circuits
50.sub.1 is connected by the FPC 56 to the back electrode 38a of
the transducer element 44a and the back electrode 38b of the
transducer element 44b, and receiving circuits 50.sub.2 is
connected by the FPC 56 to the back electrode 38c of the transducer
element 44c and the back electrode 38d of the transducer element
44d.
Moreover, the transmitting-circuit unit 48 and the
receiving-circuit unit 50 are connected by a connector 52 provided
in the ultrasonic probe 40 to a control circuit 62, a
signal-processing circuit 64 and a display 66, all incorporated in
the ultrasonic diagnostic apparatus 60.
The control circuit 62 provided in the ultrasonic diagnostic
apparatus 60 controls the ultrasonic probe 40. The
signal-processing circuit 64 receives, via the connector 52, a
signal generated by a transducer 44 of the probe 40. The circuit 64
performs analog-to-digital conversion on the signal, generating a
digital signal. The digital signal is supplied to the display 66
that is, for example, a CRT monitor. The display 66 therefore
displays a tomogram after an envelope, for example, has been
detected.
During the signal transmission, the receiving circuits 50.sub.1 and
50.sub.2 remain short-circuited. The return currents supplied from
the two transmitting circuit 48.sub.1 and 48.sub.2 therefore flow
through the associated receiving circuits 50.sub.1 and 50.sub.2,
respectively. However, the back electrodes 38 are at a potential
equal to the ground potential (GND) because a potential difference
scarcely develops between the receiving circuits 50.sub.1 and
50.sub.2. During the signal reception, the transmitting circuit
48.sub.1 and 48.sub.2 remain at a constant voltage. The
transmitting circuit 48.sub.1 and 48.sub.2 are therefore set at a
potential equal to the ground (GND) potential in terms of
alternating current and are disconnected in terms of direct current
due to the insulating property of the ultrasonic transducer unit.
In the present embodiment, the transmitting circuit 48.sub.1 and
48.sub.2 may not be at the GND potential during the reception.
Nonetheless, the transmitting circuit 48.sub.1 and 48.sub.2 receive
no influence even if they remain at different potentials.
FIG. 6 is a perspective view showing a different ultrasonic
transducer unit that may be incorporated in the two-dimensional
array ultrasonic probe according to the first embodiment.
As shown in FIG. 6, the ultrasonic transducer unit 30a of the
two-dimensional array ultrasonic probe comprises a backing material
32, a plurality of ultrasonic transducer elements 34, and a
plurality of acoustic adjustment layers 70. The transducer elements
34 and the acoustic adjustment layers 70 are arranged on the
backing material 32, in the form of a two-dimensional lattice.
Electrodes are provided on the acoustic emission surfaces of the
elements 34, and other electrodes are provided on the backs of the
elements 34, which contact backing material 34. These electrodes
are connected to transmitting circuits (not shown) and receiving
circuits (not shown). The acoustic adjustment layers 70 may be of
the type that has an acoustic member such as an acoustic lens or a
bio-contact member.
In any other structural respect, the ultrasonic transducer unit 30a
is identical to the ultrasonic transducer unit 30 (FIG. 3) of the
two-dimensional array ultrasonic probe. Therefore, the components
identical to those of the unit 30 are designated by the same
reference numbers and will not be described in detail.
The operating principle and advantages of the ultrasonic transducer
unit according to the present embodiment will be described.
FIGS. 7A and 7B are plan views representing patterns in which the
electrodes are arranged in the two-dimensional array probe
according to the first embodiment, FIG. 7A showing the electrode
pattern on the acoustic emission surface (i.e., transmission side),
and FIG. 7B showing the electrode pattern on the back (i.e.,
reception side).
These electrode patterns correspond to an arrangement of
transmitting elements and an arranged of receiving elements,
respectively. As FIG. 4, FIG. 7A and FIG. 7B show, the
acoustic-emission electrode 36 are arranged in the X-direction at
the same pitch the piezoelectric element 34 are arranged, and in
the Y-direction at twice the pitch the piezoelectric element 34 are
arranged. The back electrodes 38 are arranged in the X-direction at
twice the pitch the piezoelectric element 34 are arranged, and in
the Y-direction at the same pitch as the piezoelectric element 34
are arranged. In this electrode pattern, the Y-direction pitch of
transmitting elements and the X-direction pitch of receiving
elements are, respectively, twice the Y- and X-direction pitches in
the conventional two-dimensional array probe described above.
FIGS. 8A to 8C are diagrams depicting the two-dimensional
directivity, i.e., sound fields, which an ordinary two-dimensional
array probe has. For the sake of explanation, the X- and
Y-directions are represented as lines that incline at a specific
deflection angle (e.g., 40), and FIGS. 8A to 8C show all quarters
of the X-Y plane each.
Each ultrasonic transducer element is connected to a transmitting
circuit and a receiving circuit, independently of any adjacent
element. Hence, each element has a delay time appropriate for its
position. Thus, as long as the transmitting circuit and the
receiving circuits have the same characteristics and the same
aperture width, the transmitting sound field shown in FIG. 8A and
the receiving sound field shown in FIG. 8B are identical to each
other. FIG. 8C shows a transmitting/receiving sound field that is a
product of the transmitting sound field (FIG. 8A) and the receiving
sound field (8B), which is given by a complex number. As seen from
FIGS. 8A to 8C, grating lobes develop, extending in the
X-direction, Y-direction and an oblique direction, respectively.
The oblique direction pertains to a structural period.
FIGS. 9A to 9C depict sound fields that are generated if two
transmitting circuits for two elements are connected in parallel in
the Y-direction as shown in FIG. 7A and two receiving circuits for
two elements are connected in parallel in the X-direction as shown
in FIG. 7B. More precisely, FIG. 9A shows a transmitting sound
field, FIG. 9B shows a receiving sound field, and FIG. 9C shows a
product of the sound field (FIG. 9A) and the receiving sound field
(9B), which is given by a complex number.
As shown in FIG. 9A, the grating lobe is intense in the Y-direction
because the transmitting elements are arranged in the Y-direction
at a pitch twice as long. The grating lobe is intense also in a
direction which is a little oblique to the X-direction, unlike the
grating lobe shown in FIG. 8A. As shown in FIG. 9B, the grating
lobe is intense in the X-direction because the transmitting
elements are arranged in the X-direction at a pitch twice as great.
This grating lobe is intense also in a direction a little oblique
to the Y-direction, unlike the grating lobe shown in FIG. 8B.
The grating lobe shown in FIG. 9A is intense in one direction,
whereas the grating lobe shown in FIG. 9B is intense in another
different direction. Hence, these grating lobes cancel out each
other. This is why no grating lobes develop in the
transmitting/receiving sound field of FIG. 9C.
Comparison of FIGS. 8C and 9C reveals that the grating lobe shown
in FIG. 9C is a little more intense than the grating lobe shown in
FIG. 8C. It should be note that the transmitting circuits and the
receiving circuits are used in half the number they are provided in
the conventional two-dimensional array probe since the electrodes
for adjacent elements are short-circuited in both the transmitting
circuits and the receiving circuits.
In view of this, consider a two-dimensional array transducer unit
that satisfies the following equations: Nx'=1.4Nx Ny'=1.4Ny
Px'=Px/1.4 Py'=Py/1.4
where Nx' is the pitch at which transducer elements are arranged in
the X-direction, Ny' is the pitch at which the transducer elements
are arranged in the Y-direction, Nx is the number of elements
forming each row extending in the X-direction, and Ny is the number
of elements forming each column extending in the X-direction.
In this two-dimensional array transducer unit, as described above,
two adjacent elements arranged in the Y-direction is short-circuit
during the signal transmission, and two adjacent elements arranged
in the X-direction are short-circuit during the signal reception.
Using this transducer unit, the two-dimensional array probe
according to the present embodiment has the same aperture width and
almost the same number of transmitting circuits and receiving
circuits as the conventional two-dimensional array probe.
FIGS. 10A to 10C are diagrams depicting the sound fields that the
two-dimensional array probe according to the first embodiment of
this invention may have. Since the elements are arranged at short
pitches, the grating lobes shown in FIGS. 10A and 10B have low
level. In the sound field of FIG. 10C, no grating lobes are
observed at all in this embodiment, unlike in the sound field of
FIG. 9C.
That is, if transmitting circuits and receiving circuits are used
in the same number and the aperture is as large as in the
conventional two-dimensional array probe, it is possible to prevent
grating lobes from developing. This means that the two-dimensional
array probe can have a larger aperture if grating lobes are allowed
to develop at the same level as in the conventional two-dimensional
array probe. The probe can therefore be improved in sensitivity and
resolution.
The present embodiment is also advantageous in that the element
pitch is about 0.7 times the element pitch of the conventional
probe, thus improving the shape ratio of the piezoelectric
elements, so long as the probe has the same aperture.
Generally, the elements are arranged in less number in the X- or
Y-direction in a two-dimensional array than in a one-dimensional
array. Therefore, each element is broader than in the
one-dimensional array. The two-dimensional array is easily
influenced by lateral vibration, i.e., unnecessary vibration. In
order to make the two-dimensional array less influenced, the
technical called sub-dicing may be employed, diving each element
along a vertical or horizontal line. If the element is divided into
two segments, however, each segment, i.e., one piezoelectric
element will be too narrow to be mechanically strong enough.
In the present embodiment, the element pitch is about 70% of the
pitch applied to the conventional two-dimensional array probe.
Hence, the elements can have not only a shape ratio that suppresses
unnecessary vibration, but also a width that ensures sufficient
strength.
Second Embodiment
A second embodiment of the present invention will be described.
FIGS. 11A and 11B are plan views representing patterns in which the
electrodes are arranged in a two-dimensional array probe according
to a second embodiment. FIG. 11A shows the electrode pattern on the
acoustic emission surface. FIG. 11B shows the electrode pattern on
the back.
In the second embodiment, the acoustic-emission electrode 36 are
arranged in the X-direction, forming two columns, and in the
Y-direction, forming three rows. Conversely, the back electrodes 38
arranged in the X-direction, forming three columns, and in the
Y-direction, forming two rows. Each acoustic-emission electrode 36
connects, by short-circuiting, six piezoelectric elements 34. Each
back electrode 38 connects, by short-circuiting, six piezoelectric
elements 34. Thus, the piezoelectric elements 34, acoustic-emission
electrode 36 and back electrodes 38 constitute a transducer unit.
This configuration of the transducer unit is desirable in the case
where the piezoelectric elements must be arrange at shorter pitches
than in the first embodiment, because of their shape ratio.
In the first embodiment, the pitches at which the elements are
arranged in the X- and Y-directions during the signal transmission
greatly differs from the pitches at which the elements are arranged
in the X- and Y-directions during the signal reception, and the
elements may be unbalanced in terms of directivity (element
factor). In the second embodiment, the pitch at which the elements
are arranged in the X-direction is similar to the pitch at which
they are arranged in the Y-direction. Hence, elements are scarcely
unbalanced in terms of directivity. The direction in which the
grating lobes extend during the signal transmission is indeed
similar to the direction in which they extend during the signal
reception. Nevertheless, the array has directivity high enough to
suppress grating lobes during both the signal transmission and the
signal reception.
In the embodiment previously described, the elements are arranged
in the form of a 1.times.2 lattice or a 2.times.3 lattice. The
elements can be arranged in any other pattern and connected by
short-circuiting. That is, this invention is characterized in that
the electrodes are arranged in a pattern on the acoustic emission
surface and in another pattern on the back. Therefore, the grating
lobes extend in one direction during the signal transmission and in
another direction during the signal reception. Any transducer unit
that has such a short-circuit pattern and such a circuit
configuration falls within the scope of the present invention.
Third Embodiment
A third embodiment of the present invention will be described.
In the first and second embodiments described above, the
acoustic-emission electrode are arrange, forming a lattice, and the
back electrodes are arranged, forming a lattice, and each
acoustic-emission electrode intersects at right angles with one
back electrode. The electrodes may be arranged in any other
pattern. In the third embodiment, the electrodes are arranged in a
zigzag pattern or in a honeycomb pattern.
FIGS. 12A to 12C show the arrangement of the transducer elements of
a two-dimensional array ultrasonic probe according to the third
embodiment of this invention. FIG. 12A is a perspective view of the
probe. FIG. 12B is a perspective view showing the electrode pattern
of the probe. FIG. 12C is a plan view showing the electrode pattern
of the probe.
As FIG. 12A shows, the transducer unit 80 of the two-dimensional
array ultrasonic probe comprises a backing material 82 and a
plurality of ultrasonic transducer (piezoelectric) elements 84. The
ultrasonic transducer elements 84 are shaped like a hexagonal prism
and are arranged on the backing material 32, in a honeycomb
pattern. Electrodes are provided on the acoustic emission surfaces
of the elements 34, and other electrodes are provided on the backs
of the elements 84, which contact backing material 82. These
electrodes are connected to transmitting circuits (not shown) and
receiving circuits (not shown). Further, an acoustic member, such
as an acoustic adjustment layer, an acoustic lens or a bio-contact
member, is arranged on the acoustic emission surface of each
transducer element 84.
FIGS. 12B and 12C show the arrangement of the transducer elements
84 shown in FIG. 12A. More precisely, FIG. 12B is a perspective
view of the electrodes, and FIG. 12C is a plan view of the
electrodes. FIGS. 12B and 12C show only the acoustic-emission
electrode 86 and back electrodes 88. In this embodiment, any two
adjacent piezoelectric elements 84 arranged in a first direction
are short-circuited by one acoustic-emission electrode 86 provided
on their acoustic emission surfaces, and any two adjacent
piezoelectric elements 34 arranged in a second direction
intersecting at right angles with the first direction are
short-circuited by one electrode 38 provided on their backs.
Transmitting circuits (not shown) are connected to the
acoustic-emission electrodes 86 and receiving circuits (not shown)
are connected to the back electrodes 88, by a signal-line board,
such as a flexible printed-circuit (FPC) board. As a result, the
two-dimensional array ultrasonic transducer unit 80 has such a
circuit configuration as shown in FIG. 5.
Since the transducer elements are shaped like a hexagonal prism and
are arranged in a honeycomb pattern, this embodiment can attain the
same advantages as the first and second embodiments and can have
higher area-use efficiency.
In the third embodiment, the transducer elements are shaped like a
hexagonal prism. Instead, the transducer elements may be
membrane-shaped ones such as capacitive micro-machined ultrasonic
transducers (CMUT). If this is the case, disc-shaped transducer
elements are arranged on a flat plate.
If the transducer unit comprises membrane-shaped transducer
elements, represented by CMUTs, it will achieve the same
advantages.
Fourth Embodiment
A fourth embodiment of the invention will be described.
The first to third embodiments, which have been described, are
two-dimensional array ultrasonic probes. Nonetheless, the present
invention can be applied to one-dimensional array ultrasonic
probes, too.
FIG. 13 is a perspective view showing the configuration of the
transducer unit of a one-dimensional array ultrasonic probe
according to a fourth embodiment of this invention.
As shown in FIG. 13, this transducer unit 90 comprises a backing
material 92 and a plurality of ultrasonic transducer elements 94.
The transducer (piezoelectric) element 94 are shaped like a
rectangular bars and arranged on the backing material 92, in one
direction. A plurality of electrodes 96 are formed on the acoustic
emission surfaces of the transducer (piezoelectric) element 94,
respectively. A plurality of electrodes are formed on the backs of
the elements 94, which contact the backing material 92. The
acoustic-emission electrodes 96 are connected to transmitting
circuits (not shown), and the back electrodes are connected to
receiving circuits (not shown). Further, an acoustic member, such
as an acoustic adjustment layer, an acoustic lens or a bio-contact
member, is arranged on the acoustic emission surface of each
transducer element 84.
FIG. 14 is a diagram depicting a sound field having a sound field
that the one-dimensional array ultrasonic probe according to the
fourth embodiment may have.
In the transducer unit 90 according to the fourth embodiment, each
back electrode (not shown) is short-circuited to one piezoelectric
element, and each acoustic-emission electrode 96 is short-circuited
to two piezoelectric elements.
The transducer unit 90 thus configured emits a main beam 100 shown
in FIG. 14. During the signal emission, grating lobes 102 develop.
During the signal reception, grating lobes 104 develop. The grating
lobes 102 developing during the signal transmission and the grating
lobes 104 developing during the signal reception differ in the
direction they extend. Therefore, they do not practically influence
an image.
Thus, the fourth embodiment can achieves the same advantages as the
first to third embodiments. Moreover, the fourth embodiment can
reduce the transmitting-circuit section and the receiving-circuit
section to half the size of the conventional circuit sections.
In the embodiments described above, the transmitting circuits are
connected to the acoustic-emission electrodes, and the receiving
circuits are connected to the back electrodes. Instead, the
transmitting circuits may be connected to the back electrodes, and
the receiving circuits may be connected to the acoustic-emission
electrodes. In this case, too, the advantages described above can
be attained.
In the embodiments described above, each of the ultrasonic
transducer elements (piezoelectric elements) is short-circuited to
an acoustic-emission electrode and to a back electrode. This
invention is not limited to this configuration. For example, the
ultrasonic transducer elements may be short-circuited to a circuit
board comprising the transmitting circuits and to a circuit board
comprising the receiving circuits.
In the embodiments described above, the transmitting circuits and
the receiving circuits are provided in the probe head. Instead,
they may be provided in the connector unit or in the main unit of
the diagnostic apparatus. In this case, too, the advantages
described above can be achieved.
Several embodiments of the present invention have been described.
Nonetheless, various changes and modifications can be made, without
departing from the scope and spirit of the present invention.
Further, the embodiments described above include various phases of
the invention. The components disclosed herein may be combined in
various ways to make various inventions. Even if some components of
any embodiment described above are not used, it is possible to
solve the problems specified in the "SUMMARY OF THE INVENTION." Any
configuration not using some components can be considered as the
invention so long as it achieves at least one of the advantages
that will be stated in the following paragraph.
The present invention can provide a two-dimensional array
ultrasonic probe that has as small a transmitting-circuit section
and a receiving-circuit section as possible and yet has a large
aperture and high sensitivity, not influenced by grating lobes, and
also an ultrasonic diagnostic system that has such a
two-dimensional array ultrasonic probe.
Since the piezoelectric elements can easily be arranged at such an
optimal pitch that they may have a desired shape ratio. The
elements can therefore be prevented from degrading in their
ultrasonic transmitting-receiving characteristic.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
* * * * *